Mold for making metal patterns by electrodeposition



' narily Patented Apr. 3, 1928.

UNITED STATES ARTHUR x. LAUREL, or person, MICHIGAN.

MOLD non MAKING METAL ra'rrnans BY ELnoriaonEros'rr-ion.

No Drawing.

This invention relates to the art of mak ing electrodeposited metal articles and more especially metal patterns for use in foundry practice wherein extreme accuracy and fidelity to a master pattern or pattern from which the electrodeposited device is reproduced is to be insured, and in the making of such patterns or devices it has been heretofore suggested to use plaster of Paris molds.

The use of such plaster of Paris molds has offered many difficulties in the past when the electrolyte in which the plating is effected has been of an acid nature, as commercial plaster of Paris contains a substantial percentage of carbonate such as of magnesium or calcium, and this carbonate is readily attacked by the acid of the electrolyte causing a disintegration of the mold in the formation of gas to an extent which prevents the proper adhesion of the plate to the surface of the mold, producing results known in the trade as kicking, in which gas accumulates between the plate and surface of the mold causing the plate to blister or bulge outwardly from such surface and thereby destroying the true form of the plate.

Ordinarily the presence of carbonate in plaster of Paris is considered advantageous as it retards the set of the plaster which is desirable in the ordinary uses in which such plaster of Paris is commonly employed as in the plastering of walls and the making of plastic casts, so that no attempt is ordimade to eliminate this carbonate. Plaster of Paris also contains a small amount of calcium hydroxide which picks up carbon dioxide during exposure to the atmosphere and calcining, thus forming calcium carbonate.

The present invention contemplates the use of a substantially carbonate free plaster of Paris for molds to be used for the production of electrodeposited articles and more particularly metal patterns whereby decomposition in the acid bath will be avoided and the objectionable formation of gas minimized to a great degree where it is practically negligible. As a consequence, such plaster of Paris will resist the action of the electrolyte much longer, will not load up the bath with magnesium salts which is an ob jectionable feature of ordinary plaster of Paris, and will permit deposition Without objectionable gas formation between the mold and the plate, thus avoiding kicking Application filed October 15, 1926. Serial in. 141,886.

and warping of the plate or metal pattern,

and also swelling and warping of the plaster itself.

-With ordinary plaster of Paris more or less success has been attained in its use by impregnating it with wax which is not however always successful, especially where the mold is subjected to a bath of relatively high acidity or for extended periods, and the waxing process is somewhat diflicult to accomplish with any degree of perfection with ordinary plaster of Paris, but by the use of substantially carbonate free plaster of Paris, waxing may be also resorted to as an additional protection against the acid of the electrolyte.

The carbonates in plaster of Paris are not difficult to get rid of to the extent required for the purposes of this invention and such elimination may be effected by treating gypsum with dilute sulphuric acid which will drive off the carbon dioxide and change the carbonate to sulphate after which the excess acid may be washed out. Also, synthetic plaster of Paris may be made of such material as bone products, comprising calcium carbonate and calcium phosphate by distilling the phosphates off in the form of phosphoric acid by adding sulphuric acid, leaving calcium sulphate and traces of carbon.

There are other methods of producing synthetic plaster of Paris known in the chemical art, many of which may be adopted for the production of a suitable substantially carbonate free plaster of Paris for the said purposes, the method of securing the substantially carbonate free plaster of Paris not being a part of the present invention which resides solely in the use of such a form of that material for the purposes hereinbefore set forth and to overcome the disadvantages appertaining to the use of ordinary plaster of Paris.

The carbonate content calculated as carbon dioxide may be as low as .075%, and with this low percentage, kicking, working, etc., will take place in ordinary plaster, so that for particular work it is proposed to keep the carbonate content below this, although within the scope of this invention, where waxing is alsoutilized as a preventive against acid attack, the carbonate content may be higher than this but substantially below that of normal plaster of Paris.

The invention although simple is extremely valuable in facilitating and making feasible many plating operations on plaster of Paris which have been unsuccessfully at-' tempted hitherto in the plating art andv which have apparently battled the ingenuity of many experimenters in the past who have attempted to use plaster of Paris for mak:

ing metal patterns or electrodeposited articles Where extreme accuracy of contour has been des rable.

ed of substantially carbonate-free plaster of Paris.

1n testimony whereof I aflix my signature.

ARTHUR K. LAUKEL. 

